NumPy pickle warnings

[j-c-c]

We have some warnings related to loading NumPy object arrays that were saved with legacy NumPy. These can be fixed by loading and re-saving with a current version of NumPy. PR to follow.

tests/test_covar2d.py: 12 warnings                                                                                              
  /scratch/jc5485/miniconda3/envs/aspire_v0.14.1_py3.12_gpu/lib/python3.12/site-packages/numpy/lib/_format_impl.py:838: Depreca\
tionWarning: numpy.core._multiarray_umath is deprecated and has been renamed to numpy._core._multiarray_umath. The numpy._core \
namespace contains private NumPy internals and its use is discouraged, as NumPy internals can change without warning in any rel\
ease. In practice, most real-world usage of numpy.core is to access functionality in the public NumPy API. If that is the case,\
 use the public NumPy API. If not, you are using NumPy internals. If you would still like to access an internal attribute, use \
numpy._core._multiarray_umath._reconstruct.                                                                                     
    array = pickle.load(fp, **pickle_kwargs)       

[j-c-c]

Resolved in #1334